There is provided a method of detecting offset in a sense amplifier of an SRAM memory unit. The method comprises using a sense amplifier of the SRAM memory unit to implement a read of a first data value stored in a memory cell of the SRAM memory unit, and measuring a first time for the sense amplifier to read the first data value. The method further comprises using the sense amplifier to implement a read of a second data value stored in a memory cell of the SRAM memory unit, and measuring a second time for the sense amplifier to read the second data value. The method then comprises calculating a difference between the first time and the second time, and determining whether an offset adjustment should be applied to the sense amplifier in dependence upon the difference between the first time and the second time.
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1. A method of detecting offset in a global sense amplifier of an SRAM memory unit, the method comprising: using the global sense amplifier of the SRAM memory unit to implement a read of a first data value stored in a memory cell of the SRAM memory unit, and measuring a first time for the global sense amplifier to read the first data value (A 2 ); using the global sense amplifier to implement a read of a second data value stored in a memory cell of the SRAM memory unit, and measuring a second time for the global sense amplifier to read the second data value (A 3 ); calculating a difference between the first time and the second time; determining that an offset adjustment should be applied to the global sense amplifier in dependence upon the difference between the first time and the second time; and wherein each memory cell is connected to both a first local bit line (LBL) and a second local bit line (LBL˜) via respective access switches that are activated by a corresponding word line (WL 0 , WL 1 , WL 2 , WL 3 ), the first and second local bit lines (LBL, LBL˜) are each operatively connected to corresponding first and second global bit lines (GBL, GBL˜) via respective local-to-global switches or a local sense amplifier.
A method for detecting offset in a global sense amplifier within an SRAM memory unit. The method involves reading a first data value from a memory cell using the global sense amplifier and measuring the time it takes (first time). It then reads a second data value from a memory cell using the same global sense amplifier and measures that time (second time). The difference between these two times is calculated. Based on this time difference, a determination is made whether an offset adjustment is needed for the global sense amplifier. Each memory cell connects to two local bit lines via access switches controlled by word lines. The local bit lines connect to global bit lines through switches or a local sense amplifier.
2. The method of claim 1 , wherein the first data value is any of a ‘1’ and a ‘0’ and the second data value is the other of a ‘1’ and a ‘0’.
The method of detecting offset in a global sense amplifier, as described where a first and second time are measured by reading data values using the global sense amplifier and comparing the difference to determine whether an offset adjustment is needed, specifies that the first data value can be either a '1' or a '0', and the second data value is the opposite value ('0' or '1' respectively). This allows for comparison of read times for different data values to detect offsets.
3. The method of claim 1 , wherein the step of using the global sense amplifier to implement a read comprises: connecting the memory cell to be read to a pair of complementary bit lines; and using the global sense amplifier to sense a voltage difference between the complementary bit lines.
The method of detecting offset in a global sense amplifier, as described where a first and second time are measured by reading data values using the global sense amplifier and comparing the difference to determine whether an offset adjustment is needed, involves connecting the memory cell being read to a pair of complementary bit lines. The global sense amplifier then senses the voltage difference between these complementary bit lines to determine the stored data value.
4. The method of claim 3 , wherein the complementary bit lines comprise the first local bit line (LBL) and the second local bit line (LBL˜), the first and second local bit lines being operatively connected to the global sense amplifier via respective first and second global bit lines (GBL, GBL˜), and the step of using the global sense amplifier to sense the voltage difference between the complementary bit lines comprises applying voltages to the first and second global bit lines (GBL, GBL˜) that correspond to voltages present on the first and second local bit lines (LBL, LBL˜) respectively and using the global sense amplifier to sense a voltage difference between first and second global bit lines (GBL, GBL˜).
The method of detecting offset in a global sense amplifier, as described where a first and second time are measured by reading data values using the global sense amplifier and comparing the difference to determine whether an offset adjustment is needed, involves using complementary local bit lines (LBL and LBL~) connected to the memory cell. These local bit lines are connected to global bit lines (GBL and GBL~) respectively. To sense the voltage difference, voltages corresponding to the local bit lines are applied to the global bit lines, and the global sense amplifier detects the voltage difference between the global bit lines.
5. The method of claim 4 , wherein the step of applying voltages corresponding to voltages present on the first and second local bit lines (LBL, LBL˜) to the first and second global bit lines (GBL, GBL˜) respectively comprises connecting the first and second local bit lines to the first and second global bit lines (GBL, GBL˜) respectively, wherein the first time and the second time are measured from the point at which the first and second local bit lines (LBL, LBL˜) are connected to the first and second global bit lines (GBL, GBL˜).
The method of detecting offset in a global sense amplifier, using local and global bit lines, as described where a first and second time are measured by reading data values using the global sense amplifier by comparing the voltage differences on complementary bit lines and comparing the difference to determine whether an offset adjustment is needed, specifies that the voltages applied to the global bit lines correspond to the voltages on the local bit lines by directly connecting the local bit lines to the global bit lines. The first and second read times are measured starting from the moment these connections are made.
6. The method of claim 4 , wherein the step of applying voltages corresponding to voltages present on the first and second local bit lines (LBL, LBL˜) to the first and second global bit lines (GBL, GBL˜), respectively comprises using the local sense amplifier to sense a voltage difference between the first and second local bit lines (LBL,LBL˜) and applying correlating/corresponding voltages to the first and second global bit lines (GBL, GBL˜), wherein the first time and the second time are measured from the point at which correlating/corresponding voltages are applied to the first and second global bit lines (GBL, GBL˜).
The method of detecting offset in a global sense amplifier, using local and global bit lines, as described where a first and second time are measured by reading data values using the global sense amplifier by comparing the voltage differences on complementary bit lines and comparing the difference to determine whether an offset adjustment is needed, uses a local sense amplifier to detect the voltage difference on the local bit lines. Voltages that correlate to those sensed by the local sense amplifier are then applied to the global bit lines. The measurement of the first and second read times begins when correlating voltages are applied to the global bit lines.
7. The method of claim 1 , wherein the SRAM memory unit comprises a plurality of memory cells, a first subset of the plurality of memory cells being available to store data and a second subset of the plurality of memory cells being available to implement first and second test read operations, and wherein the memory cell used to store the first data value and the memory cell used to store the second data value being part of the second subset.
The method of detecting offset in a global sense amplifier, as described where a first and second time are measured by reading data values using the global sense amplifier and comparing the difference to determine whether an offset adjustment is needed, uses an SRAM memory unit containing multiple memory cells. Some cells are used for regular data storage, while others are dedicated to the test read operations that measure the first and second read times. The data values used for measuring the first and second times are read from these dedicated test cells.
8. The method of claim 7 , wherein the first and second test read operations are implemented when the SRAM memory unit is in a calibration mode.
The method of detecting offset in a global sense amplifier, using dedicated memory cells to measure first and second read times as described in the previous test, executes the test read operations (reading the first and second data values and measuring the times) when the SRAM memory unit is in a special calibration mode. This isolates the testing process from normal operation.
9. The method of claim 8 , and further comprising applying an offset adjustment to the global sense amplifier.
The method of detecting offset in a global sense amplifier, as described in the previous calibration mode tests, further includes actually applying an offset adjustment to the global sense amplifier. If the time difference between reading the '1' and '0' indicates an offset, the amplifier's bias is adjusted to compensate.
10. The method of claim 9 , wherein the SRAM memory unit has a hierarchical bit line arrangement and the offset adjustment is applied to both the local sense amplifier associated with the memory cell used for the first and second test read operations and the global sense amplifier.
The method of detecting offset and adjustment in a hierarchical SRAM, as described in the previous calibration mode and offset adjustment steps, involves both a local sense amplifier (near the memory cell) and the global sense amplifier. The offset adjustment is applied to both the local sense amplifier associated with the memory cell used for the testing, as well as the global sense amplifier.
11. The method of claim 9 , wherein the step of determining that the offset adjustment should be applied to the global sense amplifier in dependence upon the difference between the first time and the second time comprises comparing the calculated difference with a threshold (A 5 - 1 ), and determining that the offset adjustment should be applied to the global or local sense amplifier if the calculated difference exceeds the threshold (A 5 - 2 , A 5 - 3 ).
The method of detecting offset and applying adjustment, as described in the previous steps, involves comparing the calculated time difference between the first and second read operations to a threshold value. If the calculated time difference exceeds this threshold, then it is determined that an offset adjustment should be applied to the global or local sense amplifier.
12. The method of claim 11 , wherein the threshold is determined based on a minimum offset adjustment that can be applied to the global sense amplifier.
The method of detecting offset and applying adjustment based on exceeding a threshold, as described in the previous step, defines the threshold by the smallest offset adjustment that the global sense amplifier can actually apply. This prevents triggering adjustments that are too fine-grained to be effective.
13. The method of claim 1 , wherein, when it is determined that the offset adjustment should be applied to the global sense amplifier, the offset adjustment is determined in dependence upon the magnitude of the calculated difference.
The method of detecting offset and applying adjustment, as described in the previous steps, specifies that when an offset adjustment is determined to be necessary, the magnitude of that adjustment is based on the magnitude of the calculated time difference between the first and second read operations. Larger time differences result in larger offset adjustments.
14. The method of claim 1 , and further comprising: for each of two or more local sense amplifiers of the SRAM memory unit that are operatively connected to the global sense amplifier, using the global sense amplifier to implement the read of a first data value and the read of a second data value via the local sense amplifier and measuring the first time for the global sense amplifier to read the first data value and the second time for the global sense amplifier to read the second data value; and determining that an offset adjustment should be applied to the global sense amplifier in dependence upon the difference between the first time and the second time measured for each of two or more local sense amplifiers.
The method of detecting offset in a global sense amplifier, as described where a first and second time are measured by reading data values using the global sense amplifier and comparing the difference to determine whether an offset adjustment is needed, is extended to include multiple local sense amplifiers connected to the global sense amplifier. The read operations are repeated for each local sense amplifier, measuring the first and second times for each. The decision to apply an offset adjustment to the global sense amplifier is based on the time differences measured across all the local sense amplifiers.
15. The method of claim 14 , wherein the step of determining that an offset adjustment should be applied to the global sense amplifier in dependence upon the difference between the first time and the second time measured for each of one or more local sense amplifiers comprises using the time difference measured for each of two or more local sense amplifiers to determine a representative time difference and using the representative time difference to determine the offset adjustment to be applied.
The method of detecting offset using multiple local sense amplifiers, as described in the previous step, determines if an offset adjustment is needed by using the time differences measured for each local sense amplifier to calculate a representative time difference. This representative value is then used to decide if an offset adjustment is required.
16. The method of claim 15 , wherein the representative time difference is any of an average and a mean of the time difference measured for each of two or more local sense amplifiers.
The method of detecting offset using multiple local sense amplifiers and a representative time difference, as described in the previous step, specifies that the representative time difference can be calculated by averaging the individual time differences, or by calculating the mean of those differences.
17. An apparatus for detecting offset in a sense amplifier of an SRAM memory unit, the apparatus comprising: a timer module configured to measure a first time for the global sense amplifier to read a first data value stored in a memory cell of the SRAM memory unit, and to measure a second time for the global sense amplifier to read a second data value stored in a memory cell of the SRAM memory unit; a memory module configured to store the first time and the second time measured for the global sense amplifier; and a detection module configured to calculate a difference between the first time and the second time; and to determine that an offset adjustment should be applied to the global sense amplifier in dependence upon the difference between the first time and the second time.
An apparatus for detecting offset in a global sense amplifier of an SRAM memory unit. The apparatus has a timer module that measures the time it takes for the global sense amplifier to read a first data value (first time) and a second data value (second time) from memory cells. A memory module stores these first and second times. A detection module calculates the difference between the first and second times and then determines whether an offset adjustment should be applied to the global sense amplifier based on this time difference.
18. The apparatus of claim 17 , wherein the detection module is configured to compare the calculated difference with a threshold, and to determine that the offset adjustment should be applied to the global sense amplifier if the calculated difference exceeds the threshold.
The apparatus for detecting offset, as described in the previous claim, includes a detection module that compares the calculated time difference to a threshold value. If the time difference exceeds this threshold, the detection module determines that an offset adjustment should be applied to the global sense amplifier.
19. The apparatus of claim 18 , and further comprising an offset adjustment module configured to cause the offset adjustment to be applied to the global sense amplifier.
The apparatus for detecting offset and making a determination to apply an adjustment, as described in the previous claims, further includes an offset adjustment module. This module is responsible for actually causing the offset adjustment to be applied to the global sense amplifier after the detection module determines it is necessary.
20. The apparatus of claim 19 , wherein the offset adjustment module is configured to determine the adjustment in dependence upon the magnitude of the calculated difference.
The apparatus for detecting offset, determining whether to apply adjustment, and then applying the adjustment, as described in the previous claims, includes an offset adjustment module that determines the *size* of the offset adjustment based on the magnitude of the calculated time difference. A larger time difference will lead to a larger adjustment.
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December 15, 2014
April 18, 2017
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